In rail wayside signal systems, incandescent light bulbs are widely used as light sources for signaling. The signaling system using incandescent light bulbs is very simple to operate and control. The incandescent light bulbs are mostly resistive loads. Therefore, the current traveling through the incandescent light bulbs is directly proportional to the input voltage. Additionally, the lighting intensity level is directly proportional to the bulbs input voltage.
With advancement in the semiconductor fields and commercialization of LEDs, applications of LEDs as replacements for incandescent light bulbs have now become a reality. Early LEDs were often used as indicator lamps for electronic devices, replacing small incandescent bulbs. They were soon packaged into numeric readouts in the form of seven-segment displays, and were commonly seen, for example, in digital clocks.
Recent developments in LEDs permit them to be used in environmental and task lighting. LEDs have many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. LEDs are now used in applications as diverse as aviation lighting, automotive headlamps, advertising, general lighting, traffic signals, camera flashes and even LED wallpaper.
One of the characteristics of the incandescent light bulbs is the almost linear relationship between the input voltage and the input current. Traditionally, the rail wayside signal system is designed to perform its signaling tasks with this linear relationship between voltage and current. LEDs do not exhibit linear relationships. Therefore, if LEDs were to be used to replace the incandescent light bulbs in existing signal systems, either the rail wayside signal system or the LEDs must be changed to ensure the safety and reliability of the rail wayside signal system.
Therefore, heretofore unaddressed needs still exist in the art to address the aforementioned deficiencies and inadequacies.